This invention relates to electromagnetic fuel injectors of the type used in internal combustion engine fuel injection systems and to methods of calibrating such fuel injectors.
Electromagnetic fuel injectors are used to control the amount of fuel that is introduced into the cylinders of an internal combustion engine. One of the important advantages of such fuel injectors is the degree of precision with which fuel can be introduced. However, to attain such precision it is necessary for the injectors to be properly calibrated.
The primary performance characteristics of injectors are: wide-open, or static, flow; dynamic flow; and linearity. Static flow is the flow achieved when the injector is energized with steady current. Dynamic flow is the flow delivered when the injector is pulsed with an electrical signal, usually measured in milliseconds. During the calibration of an injector, static flow is established by adjusting the injector's orifices, normally consisting of a fixed orifice and a variable orifice in series. The latter orifice is defined by the injector's valve lift which is adjustable. After the static flow has been established for the injector, the dynamic flow is set by loading a spring against an armature until a desired dynamic flow is achieved, and then locking the adjustment mechanism. Spring loading of the armature adjusts the opening and closing times of the injector, but does not affect the static flow.
The present invention relates to the calibration of the dynamic flow of an electromagnetic fuel injector. Calibration is attained by removing or adding magnetically permeable material to the magnetic flux path to thereby establish the opening and closing times that determine the dynamic flow. This novel method involves creating in a stationary part of the injector's magnetic circuit, a blind hole of a depth that will produce the desired dynamic flow. The appropriate depth for the blind hole can be created in either of two ways. One, by drilling a blind hole to the appropriate depth, and two, by drilling a principal hole to a depth greater than that of the appropriate depth, and then partially filling the principal hole until the appropriate depth is attained.
The invention offers significant advantages over prior techniques. The conventional prior technique for dynamic flow calibration requires an O-ring to seal the moving part which adjusts the spring force, a push pin, and some means of locking the adjustment mechanism. With the present invention that O-ring can be eliminated, yielding improved reliability and reduced cost by part elimination. The capability for achieving very good calibration accuracy is present because the diameter and depth of the blind hole can be closely controlled. The predictability of the adjustment could allow for group adjustment of injectors after their initial performance has been established.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will become apparent in the following detailed description and claims which are accompanied by drawings of a presently preferred embodiment of the invention in accordance with the best mode contemplated at this time for carrying out the invention.